Prevalence of Carbapenem Resistant Non-Fermenting Gram Negative Bacterial Infection and Identification of Carbapenemase Producing NFGNB Isolates by Simple Phenotypic Tests

INTRODUCTION

Non-Fermenting Gram negative bacilli (NFGNB) are emerging multi-drug resistant pathogens causing nosocomial infections. In recent years, carbapenem resistance in NFGNB has increased due to a variety of drug resistance mechanisms, the most common being production of carbapenemases.

AIM

To detect carbapenemase and metallo-β-lactamase (MBL) production in NFGNBs by four phenotypic tests and to compare the various phenotypic methods for detection of carbapenemase and MBL production in nosocomial NFGNB isolates.

MATERIALS AND METHODS

It is a cross sectional study carried out in the department of Microbiology, Chennai Medical College Hospital and Research Center, Irungalur, Trichy between January 2015 and December 2015. Out of the 598 NFGNB isolated from all the 5402 heterogenous clinical samples that were processed, 52 (8.7%) NFGNB showed resistance or intermediate sensitivity to meropenem as tested by disc diffusion assay. All the 52 isolates were subjected to four different phenotypic tests for carbapenemase and MBL detection, which included Modified Hodge Test (MHT), Meropenem-EDTA Disc Synergy (EDS) test, Meropenem-EDTA Combined Disc Test (CDT) and Growth on CHROMagar KPC.

RESULTS

Among the 52 isolates, 29 (55.77%) were MHT positive and 49 (94.23%) were positive for growth on CHROMEagar KPC which were identified as carbapenemase producers. 44 (84.61%) were EDS positive and 46 (88.46%) were CDT positive which were identified as metallo-β-lactamase producers.

CONCLUSION

The presence of these resistant bugs strongly suggests the need to prevent their further spread by implementation of strict infection control measures and regular surveillance to check their outcome. Growth on CHROMagar KPC is the test that has picked up more number of carbapenem resistant isolates as carbapenemase and metallo-β-lactamase producers among the four tests. It is also cheap and easy to perform, making it the most reliable test for routine screening of carbapenemase and MBL producers in clinical laboratories.

Identification of Klebsiella pneumoniae Carbapenemase-producing Klebsiella oxytoca in Clinical Isolates in Tehran Hospitals, Iran by Chromogenic Medium and Molecular Methods

OBJECTIVES

Production of carbapenemase, especially Klebsiella pneumoniae carbapenemases (KPC), is one of the antibiotic resistance mechanisms of Enterobacteriaceae such as Klebsiella oxytoca. This study aimed to investigate and identify KPC-producing K. oxytoca isolates using molecular and phenotypic methods.

METHODS

A total of 75 isolates of K. oxytoca were isolated from various clinical samples, and were verified as K. oxytoca after performing standard microbiological tests and using a polymerase chain reaction (PCR) method. An antibiotic susceptibility test was performed using a disc diffusion method according to the Clinical and Laboratory Standards Institute guidelines. CHROMagar KPC chromogenic culture media was used to examine and confirm the production of the carbapenemase enzyme in K. oxytoca isolates; in addition, PCR was used to evaluate the presence of bla_KPC gene in K. oxytoca strains.

RESULTS

Of a total of 75 K. oxytoca isolates, one multidrug resistant strain was isolated from the urine of a hospitalized woman. This strain was examined to assess its ability to produce carbapenemase enzyme; it produced a colony with a blue metallic color on the CHROMagar KPC chromogenic culture media. In addition, the bla_KPC gene was confirmed by PCR. After sequencing, it was confirmed and deposited in GenBank.

CONCLUSION

To date, many cases of KPC-producing Enterobacteriaceae, in particular K. pneumoniae, have been reported in different countries; there are also some reports on the identification of KPC-producing K. oxytoca. Therefore, to prevent the outbreak of nosocomial infections, the early detection, control, and prevention of the spread of these strains are of great importance.

Efficacy of an Enrichment Media for Increasing Threshold for Carbapenem-Resistant Enterobacteriaceae Screening

BACKGROUND

Identification of carbapenem-resistant Enterobacteriaceae (CRE) is complex and a major laboratory challenge; clinical cultures may diagnose only some of the CRE carriers among patients, thus it is crucial to perform asymptomatic carriage screening.

MATERIALS AND METHODS

 We compare the efficacy of a rectal sample culture prior to enrichment with BHI (Brain Heart Infusion) Broth and following 18-24 h. All rectal samples were applied on CHROMagar KPC selective growth media and then seeded on MacConkey agar selective growth media with an applied disk of Imipenem antibiotic on top of the media, then inserted into enrichment BHI Broth. After 18-24 h incubation with enrichment media, all samples were applied again on this media.

RESULTS

From the 2,245 rectal samples, CRE colonies were found in 96 (4.3%). Following enrichment with BHI Broth, CRE colonies were found in 111 (4.9%) CHROMagar KPC plates and 106 (4.7%) MacConkey agar.

CONCLUSION

We were able to demonstrate that the number of CRE-positive results increased due to use of additional enrichment with BHI Broth. Therefore, we recommend applying this method of addition of liquid enrichment media as part of a culture protocol routine for CRE screening.